Thrissur city functioned as a municipality since 1921 under the Cochin Municipal Regulations. In 1932, the new corporation building was constructed, and in 1972 new areas from other Panchayats were added to the municipality. On 1 October 2000, the municipal town was upgraded to the level of a Municipal Corporation with the Panchayats of Ayyanthole, Koorkkenchery, Nadathara, Vilvattom (part), Ollur and Ollukkara. The Corporation comprises three legislative assemblies Thrissur, Ollur and Cherpu. The city is administered by the Thrissur Municipal Corporation, headed by a mayor. The corporation is the second-largest city corporation in the state of Kerala in India. The city is the only local body in Kerala which directly controls power, water supply and solid waste management system in the city.

For administrative purposes, the city is divided into 52 wards, from which the members of the corporation council are elected for five years. The corporation has its headquarters in Thrissur city. The Thrissur Urban Development Authority and Town and Country Planning Department (TCPD) are the agencies that prepare development plan for the city.

The city is the headquarters of Thrissur City Police and Thrissur Rural Police. The Thrissur City Police is headed by a Police Commissioner, an Indian Police Service (IPS) officer. The city is divided into two sub divisions, Thrissur and Guruvayur. It also operates 14 police stations, including a woman police station and a traffic police station.

The Thrissur City Police Commissionerate operates out of the erst-while District Armed Police headquarters at Ramavarmapuram. The Thrissur Rural Police has its headquarters at the District Collectorate complex at Ayyanthole. The city is also the headquarters of Inspector General of Police, Thrissur Range, which looks after the law and order of Thrissur District, Palakkad District and Malappuram district. All the Superintendent of Police of these three districts come under his jurisdiction. The city also contains the Kerala Police Academy, Central Prison, Viyyur, Police Dog Training Centre and Excise Academy and Research Centre. Indian Reserve Battalion, new commando unit of Kerala Police is headquartered in Ramavarmapuram. Border Security Force (148 battalion) have its first centre in Kerala in Thrissur.